Acoustical ceiling panels



Feb. 25, 1964 R. w. BOL-rz ETAL ACOUSTICAL CEILING PANELS Filed March2l, 1960 IN V EN TORS T MQW m 550w MMW s T Tf. T P1. rLL B/ www Y UnitedStates Patent O 3,122,216 ACOUSTICAL CEILING PANELS Robert W. Boltz, SanJose, Calif., and Willis M. Rees, Newark, Ohio, assignors toOwens-Coming Fiberglas Corporation, Toledo, Ohio, a corporation ofDelaware Filed Mar. 21, 1960, Ser. No.r 16,308

5 Claims. (Cl. 181--33) The invention relates generally to soundabsorbing panels or acoustical tiles for mounting upon walls or in*stalled upon yor to form ceiling structure. The invention pertainsparticularly to ceiling panels adapted for rnechanieal suspension assound absorbing and transmission reducing media above adjacent rooms.

Such acoustical panels are customarily compressed boards of wood fibers,shredded wood, Wood pulp, cane fibers, cork granules, gypsum, rock woolor glass fibers. A popular size is twelve by twelve inches in broaddimensions and one-half inch thick. The panels are also avail# able inthicknesses up to two inches and with planar dimensions in multiples oftwelve inches. y

Those of light lweight when no larger than twelve inches square are mostcommonly attached directly to wall and ceiling surfaces by spots ofadhesive. Staples and nails are frequently employedr forsecuring inplace the heavier and broader units to furring stnips.

In ceiling treatment the vacoustical panels may be installed upon a gridsuspension system hung below the permanent ceiling structure. Thisarrangement may improve the dimensional proportions of a room as well asadd to the attractiveness of the ceiling. The air space above thesub-ceiling of panels contributes to the sound absorbing properties ofthe installation.

In business offices, such a suspended acoustical ceiling is interruptedby partitions between rooms which extend up to but generally not abovethe level of the panels. F or purposes of preserving the privacy of theindividual office areas, the intervening partitions should be of anature to reduce transmission therethrough preferably as much asthirty-five decibels. This rating indicates a loss in transmissionsuiiioient to reduce the loudness level from one side to the other sideof the wall the specied number of decibe-ls. n

Decibel units are conventionally used to roughly indicate the responsebythe ear to noise yand are equal in number Ito ten times the logarithmof the ratio of the intensity of the sound in watts per squarecentimeter to the standard reference intensity of -16 watts per squarecentimeter at thelow l-imit of human perception.

y Of the various commercial acoustical products available, those ofmineral fibers, particularly glass fibers are most highly regarded.Their `sound absorption is very effective because ,of the porosityderived from the high number of communicating air cells in the maze offibers. In contrast to panels of organic components, they arenon-combustible and unaffected by moisture. They also have the advantageof being comparatively light iu weight as well as having superior soundabsorbing capacity.

When' acoustical panels are applied to walls and directly upon a ceilingsurface, the transmission of sound energy through the panels isordinarily not of too serious a natu-re as the further travel of thesound is quite effectively curtailed by the mass of the structures uponwhich they are mounted.

However, where the panels are suspended below the regularrceiling, thereis normally nothing to interfere with the continued upward movement ofsound wavesutraveling through the panels. This piercing action may notbe too serious with the more solid type of panels such as the morecompacted organic products and those of gypsum asthese panels are not soeasily penetrated by waves.

3,122,216` Patented Feb. 25, 1964 wardly from the panels covering oneroom upon impinging against the surface of the permanent ceiling are reytiected down and enter the adjacent room through the panels thereover.-If of suflici'ent intensity, ythe overall transmitted sound may notonly ybe annoying, but may also carry conversation of a confidentialnature.

This problem may be minimized by backing the panels of glass fibers withother material such as gypsum ork other heavy plaster boards. kThe soundmovement is thus considerably reduced.k ,Howeveiy the added cost of theextra material and labor is objectionable. f

It is accordingly a prime object of this invention to provide a lowcost, light weight acousticalv panel of minera-l fibers, and onepreferably vof `glass iibers, adapted yfor mechanical suspension Vand'which adequately deters the transmission of sound waves while retainingexcellent properties of sound absorption.

More particularly, it is an object of this invention to provide a panelof mineral fibers which has on its rear face an integrated imperviousmembrane.

:Another object of this invention is to provide ceiling treatment foradjoining rooms in which panels of mineral fibers, having a sealingmembrane on their rear faces, are suspended below a common airspace'above such adjoining rooms.

It is a further object of the inventionv to provide an acoustical panelof bonded mineral fibers having an impervious membrane attached to itsrear -face and to the side edges thereof, the membrane being of a`character to block the passage of sound waves therethrough and alsoyfrom the edges thereof into adjoining panels.

Another object of the invention is to provide au acoustical panel forinstallation below an air plenum, said panel having a membrane on itsrear face not only capable of blocking movement of sound ywavestherethrough, but also tightly impervious to air whereby the plenum maybe u-sed for a supply chamber or passage for air in a Ventilatingsystem. n f

The objects of this invention are primarily attained through the placingof a membrane on the back side of otherwise standard types ofyacoustical panels of bonded glass fibers. More specifically, the objectsof the invention are secured by uniformly adhering an elastic andimpervious membrane to the rear face and side edges of an acousticalpanel.

The invention will be more fully understood and further objects andadvantagesvthereof'will become morek apparent with reading of thedetailed description which follows and referring to the accompanyingdrawings, in which:

FIGURE 1 is a side elevation, with a portion shown in vertical section,of an yacoustical panel embodying this invention; f v

HGURE 2 is a similar showing of an acoustical panel of a modified formembodying the invention; and

FIGURE 3 is a perspective View through a vertical section of twoadjoining rooms over which panels of the invention have been suspendedto form a sub-ceiling.

Referring to the drawings in more detail, the panel of FIGURE 1 has amain body portion 12 composed of bonded glass fibers. From thestandpointof lightness and acoustical effectiveness of the body portion12, glass fibers of a diameter in the range between twelve andtwenty-two hundred-thousandths of an inch serve most satisfactorily.

Fibers of still smaller diameters would enhance some properties of theproduct, while fibers of larger diameters, up to more than seventyhundred-thousandths, give quite adequate results and may be morepractical for some commercial purposes.

The size of the fibers is determined by the type and control of theforming equipment utilized. Such apparatus ordinarily employs air, steamor combustion gases for attenuating molten threads of glass issuing fromsmall orifices. The fibers lare collected at the forming station inblanket form with an uncured binder component dispersed therethrough.

A resin combination of melamine and phenol formaldehydes, in aproportion of roughly one to two, constitutes a very satisfactorybinder. The amount of binder may run between nine and twenty-six percentby weight of the finished panel, depending upon the balance desiredbetween strength and fire protection in the product. Various otherfibrous glass bonding agents are well known and would be quite equallyeffective. These include epoxy, urea, and polyester resins.

The density of the fibrous body portion of the panels generally runsbetween nine and fourteen pounds per cubic foot as compared withdensities from fifteen to twenty-four pounds per cubic foot for thepanels of compressed cellulosic fibers.

Upon the upper or back surface, and also upon the side edges of thepanel shown in FIGURE l, is a membrane 14 which is preferably analuminum foil which is firmly attached to the main body 12 by anadhesive 15. The membrane tightly seals the rear face and edges of thepanel.

For the purpose of this invention, the membrane f4 should benon-vibratile, of an elastic nature yand thoroughly adhered to thepanel. It should further be strong and fully impervious to air.

The membrane may be composed of a metal film such as an aluminum foiladhesively attached tothe body of the panel. An aluminum foil with athickness of about four ten-thousandths of an inch serves verysatisfactorily. The adhesive providing such attachment may be separatelyapplied or be a thermoplastic film such as polyethylene previouslyjoined through tissue to the metal foil. This laminate may be attachedto the panel by hot pressing.

Alternately, the membrane may be an elastic, synthetic plastic sheet offilm, either self adhered through heat treatment or adhered with anintermediate adhesive. Plastic films which have the desired qualities ofelasticity and strength include the non-rigid, vinyl chloride polymersand copolymers, vinyl chloride polymer-nitrile rubber blend, andpolyethylene. Such films are preferably at least five thousandths of aninch in thickness.

An adhesive which functions well in this service is an elastomer cementtype having a synthetic rubber base in a somewhat higher proportion of aketone solvent. It has high strength and excellent adhesion and isresistant to vinyl plasticizers, oil and other aliphatic hydrocarbons.Various other thermoplastic, thermosetting and elastomeric adhesiveswould perform quite effectively and are available in liquid formpermitting their application by spray or roller. Care should be taken toinsure uniform attachment of the membrane to the panel.

The opposite or front face of the panel may be covered with a porousfilm of paint with decorative 4and light reflecting properties. Thispaint has little resin, latex or other binding components as thoseingredients would tend to make the coating impervious to air. Porosityis required to permit the entry of sound waves into the absorbing panelof glass fibers.

Cil

The alternate form of panel shown in FIGURE 2 has a main body 18 and aback sealing membrane 20 shown adhered to the body 18 by an adhesivelayer 21. This panel does not have the sound shielding extension 16 ofthe plastic film or metal foil on the side edges thereof as does thepanel of FIGURE 1.

In FIGURE 3 is illustrated two adjacent rooms 24 and 25 separated by apartition 27. As shown each room has a tile flooring 28 laid upon a woodsub-fiooring 29 supported upon joists 30. The partition 27 will beconsidered to have outer layers 31 composed of metal l-ath and limeplaster applied against wood studs 32.

The permanent ceiling 34 has an upper covering or roof 3S laid on planks36, the latter being supported upon joists 33. A sub-ceiling utilizingpanels of this invention is suspended above each of the rooms 24 and 25below the top edge of partition 27.

The panels 4.0 installed in room 24 are of the type illustrated inFIGURE 1 having a back side and edge sealing membrane. The panels 42mounted in room 25, for purposes of illustration, are of the design ofthe panels depicted in FIGURE 2.

The panels in both rooms are supported on inverted T-bearns 45 which areheld in place by wires 47 from the joists 38. The panels are `supportedalong the partition by angled brackets 48.

It will be presumed that the partition 27 is in itself a satisfactorysound barrier between the rooms 24 and 25. As constructed with woodstuds and with metal lath and lime plaster, this wall may have atransmission loss in the region of thirty-five decibels'. Thiscurtailment of sound travel is sufiicient to reduce the noise level ofloud conversation to that of quiet whispering. It would also be theequivalent to the difference between the level of an office withtypewriters and that of a quiet living room.

Since the partition 27 does not extend up to and join the standardceiling 34, sound would travel between the rooms above the partitionunless this transmission path is otherwise blocked.

As previously stated conventional acoustical panels of mineral fibersare not effective as a barrier for this purpose. However, with thepanels fifi and 42 constructed according to this invention installed inthe suspended ceiling, a sound transmission loss approaching thatprovided by panels two or three times as heavy may be attained in thisarea without impairing the function of the fibrous glass panels inserving as excellent sound absorbing media.

It should be considered, however, that there are two separate ceilingsof the suspended back-sealed panels through which sound must pass ineither direction and that their suppression action is additive with eachcontributing an important part.

Either with or without the back sealing layers upon the panels, thetransmission loss would vary depending upon the size of the upper airspace and the nature of materials of the standard ceiling, but withoutthe back sealing layers the loss might be no more than fourteendecibels.

It may be concluded therefore that the addition of the sealing membranemay be employed to increase the sound transmission loss through thisoverhead path as much as two or three hundred percent. This transmissionloss is superior to that accompanying the use of the ordinary, lessabsorbent panels of organic fibers. At the same time the sealed panelsof mineral fibers retain their original light Weight, and their superiorsound absorbing performance is affected, at most, to only a slightdegree.

It is natural that better noise isolation is secured with acousticalpanels back-sealed according to this invention with base panels ofincreased thickness. This is due to the greater absorption provided bythe extra depth. Also, heavier sealing membranes slightly improve thesound shielding action of the panels because of the added mass.

Experience has shown that reduction of sound transmission is obtained byincreasing the mass per unit area of a partition, by constructing thepartition of material having a large resistance to bending, or by theuse of double partitions, vibrationally isolated.

The addition of mass to the sealing layers of the panels of thisinvention has, of course, limited possibilities. Reliance on effectiveperformance has been placed principally on constructing the sealingmembranes with low vibratile properties. Also it is concluded that thetwo separate ceilings of the back sealed panels contribute totransmission reduction by acting as double partitions, vibrationallyisolated. f

The side edge coverings 16 reduce direct sound transmission and make thepanel installation more impervious to air movement. This is particularlyadvantageous if the space above the panels is used as a chamber orpassage for Ventilating air. Should the space be employed as a path forheated or cooled air, the reflective heat insulating properties of themetal foil backing is ot value. Besides their acoustical and thermalproperties, thefinembranes prevent the settling of dust through thepanels.

As previously set forth herein, the membranes must be impervious and beas non-vibratiie as possible in order not to transmit sound energy. Boththe metal foil and plastic ilms have negligible gas permeability. Theplastic membranes are generally orP an elastic nature which opposesvibration in response to sound pulsations while the metal foil is heldagainst vibration by the polyethylene ilm or other elastic adhesive bywhich it is uniformly secured to the panel. The adhesives which may beused With the plastic films also may contribute to their resistance tovibrational forces.

While the invention has been described in connection with panels havinga porous, decorative coating of paint deposited on the outer facing, itis also quite equally suitable for panels having a tight, Washable outercoating of paint with spaced holes, through which sound Waves areadmitted. Likewise,fthe rear sealing membrane may be applied to panelsfaced with an unattached lilmwhich transmits sound by vibration to apanel interior as Well as to panels with the outer facing left unnished.

Having described the invention in detail and with reference toparticular materials, it willbe understod that such specifications aregiven for the salie of explanation and various modications andsubstitutions other than Weclaim:

1. An acoustical panel adapted for installation in closely abuttingrelation having a main, generally rigid and self-sustaining, porous bodyot mineral fibers integrated by a hard, non-elastic resinous binder, asound admitting surface on the front planar side of the body and an airimpervious, non-vibratile, sound backing membrane continuously andelastically attached to the rear planar side of the main body of mineralfibers.

2. An acoustical panel according to claim 1 in which the membrane iscomposed of an elastic, polymerized resin material.

3. An acoustical panel according to claim 1 in which the membraneextends down and is continuously attached to the side edges of the body.

4. An acoustical panel according to claim 1 in which l the membrane isattached to the body byran elastic synthetic resin, distinct from theresinous binder by which the main porous body is integrated.

5. An acoustical panel according to claim 4 in which the membrane is analuminum foil less than one mil in thickness.

References Cited in the file of this patent UNITED STATES PATENTS Re.24,658 Hollister inne 16, 1959 1,900,369 Smith Mar. 7, 1933 1,926,679Kellogg Sept. 12, 1933 1,950,420 Stitt Mar.13, 1934 2,022,161 SpaffordNov. 26, 1935 2,028,180 Arnold Jan. 21, 1936 2,046,296 Roos et al June30, 1936 2,177,393 Parkinson Oct. 24, 1939 2,221,001 Lucius Nov. 12,1940 2,802,764 rSlayter Aug. 13, 1957 2,838,806 Sabine lune 1'7, 19582,920,357 Ericson Jan. 12, 1960 2,990,027 Sabine June 27, 1961 3,021,916Kemp Feb. 20, 1962 3,058,411 Hanson et al Oct. 16, 1962 n 3,070,851Stephens Jan. 1, 1963 y OTHER REFERENCESk y' n Germany, application1,044,384, printed Nov. 20. 1958.

1. AN ACOUSTICAL PANEL ADAPTED FOR INSTALLATION IN CLOSELY ABUTTINGRELATION HAVING A MAIN, GENERALLY RIGID AND SELF-SUSTAINING, POROUS BODYOF MINERAL FIBERS INTEGRATED BY A HARD, NON-ELASTIC RESINOUS BINDER, ASOUND ADMITTING SURFACE ON THE FRONT PLANAR SIDE OF THE BODY AND AN AIRIMPERVIOUS, NON-VIBRATILE, SOUND BACKING MEMBRANE CONTINUOUSLY ANDELASTICALLY ATTACHED TO THE REAR PLANAR SIDE OF THE MAIN BODY OF MINERALFIBERS.